The lever that is inside the door and hooks on the rod that comes up from the latch. When it breaks it still looks find from the outside, it's underneath - inside where it breaks. At least that is what happened to mine.
The plastic I think gets brittle over time and all it takes is someone to pull a little too hard on it and 'tink!'.
The aftermarket ones I got are metal so I think they should hold up better.
------------------
'92 GT conv.
TFS heads, GT40, Powerdyne 9#, AOD, 3.73
My Mustang Page